FLUORESCENCE EXCITATION-SPECTRA OF JET-COOLED 9-HYDROXYPHENALENONE DERIVATIVES - EFFECTS OF SYMMETRICAL SUBSTITUTION ON DEUTERIUM ATOM TUNNELING

The fluorescence excitation spectra of symmetrically substituted 5-bro mo-9-hydroxyphenalenone-d, 5-chloro-9-hydroxyphenalenone-d, and 5-meth yl-9-hydroxyphenalenone-d have been measured in helium jets, The 0(0)( 0) tunneling doublet splittings of the three molecules have been deter mined, A comparison of these splittings with that of 9-hydroxyphenalen one-d suggests that electron releasing from the Br or Cl atom to the p henalenone ring significantly decreases the potential energy barrier t o tunneling in the S-1 state.